The present invention relates generally to calibration systems. More particularly, the present invention relates to a calibration tool for a laser air particle counter.
Laser air particle counters are currently used in a variety of industries. For example, many optical particle counters are used for monitoring a level of contamination in clean room facilities.
Many types of particle counters include a laser beam which, when coming into contact with an air particle, sends a signal to a tabulation device which keeps track of the number of particles that are registered during a given amount of time. Several particle counters also include methods of not only counting the number of particles that pass through a laser beam, but also registering the size of individual particles and the density of particles in varying locations of a room. Such devices are particularly important in clean rooms where highly sensitive equipment is being manufactured. Additionally, particle counters can be heavily relied upon in hospital operating rooms or medical facilities where biotechnological innovations are being investigated and developed. In such locations, it is extraordinarily important that the particle counters operate as accurately and precisely as possible; even a slight degree of error in the particle counter could result in massive contamination. This can cause a product of manufacture to contain undesirable defects and, in the case of a hospital operating room, can result in an increased amount of infection and medical complications for patients.
Additionally, even highly accurate and precise particle counters often need to be checked and calibrated to ensure that the particle counters maintain a high degree of reliability. Furthermore, particle counters need to be checked on a regular basis to determine whether or not the counter needs to be replaced.
For the above reasons, entities that manufacture and use particle counters also use calibration systems to monitor the accuracy and preciseness of their particle counters. Calibration systems are operatively connected to the particle counter and release particles of a known size and at a known rate into the particle counter. The particle counter proceeds to count the number and size of these particles and this number is compared to a size and number of particles that were released according to the calibration system. If there is a difference between the two devices that is outside of an acceptable error range, the user is able to determine whether it is necessary to repair and/or replace the particular counter.
One common type of calibration system includes one or more chamber of polystyrene latex spheres (PLSs). In each chamber all of the polystyrene spheres have a known size. When calibration is desired, the calibration system is coupled to the particle counter, and the polystyrene latex spheres are released from one of the chambers at a known rate. A nebulizer entrains the polystyrene spheres into a fine spray, and the polystyrene latex spheres are counted by the particle counter. The size and number of particles that are recorded by the particle counter are then compared to the known quantities from the calibration system.
Although such calibration systems are useful, they also include a number of drawbacks. For example, polystyrene latex spheres must often be purchased separately from a third party. Furthermore, polystyrene spheres of different sizes must also be purchased and often stored separately. Additionally, such calibration systems that include multiple chambers of polystyrene spheres can become relatively large and cumbersome. The systems may also require frequent and repetitive cleaning after a certain number of uses. Finally, nebulizers used with such calibration systems are often relatively expensive to manufacture and/or purchase.
The present invention provides for a calibration tool utilizing thermal inkjet printing technology. A closed chamber includes an inlet for receiving clean air or another gaseous substance and an outlet that is operatively connected to the chamber. A solution of a liquid carrier is coupled to the chamber, and the chamber also includes an array of thermal inkjet heads with each head including different sized orifice plate openings. The liquid carrier passes through the array of thermal inkjet heads and combines with the air entering the chamber to form a fine spray. A controller regulates the rate at which individual particles pass through the array and also regulates whether certain orifice plate openings are opened or closed.
Another aspect of the invention provides for a particle counter calibration system comprising a calibration chamber including an air intake portion for transferring a stream of a gaseous substance, and an array of inkjet heads including a plurality of orifices of different sizes. A supply of a liquid carrier is operatively connected to the chamber, and a control unit is operatively connected to the array of plates and the supply of liquid carrier. The liquid carrier passes through the array to form a plurality of liquid particles flowing through the chamber, and the size of the liquid particles and the rate at which particles exit the array are regulated by the control unit.
Another aspect of the invention provides for a system for calibrating a particle counter comprising an inlet passageway for receiving a gaseous material. A chamber is operatively connected to the air inlet passageway and includes an array of inkjet heads having orifices of different sizes. A reservoir supplies a liquid material to the chamber. A particle counter is operatively connected to the chamber, and means for controlling the number of liquid particles that exit the array are coupled to the chamber. When the liquid material is combined with the gaseous substance, a plurality of liquid particles is formed and flows through the chamber. The controlling means regulates the size of the particles and the rate at which the particles exit the array and enter the particle counter.
The present invention allows for the use of thermal inkjet droplets which are much less expensive than polystyrene latex spheres while also permitting the calibration tool to be smaller in size and also reducing the need for regular cleaning of the equipment.